Oxidative method of separating plutonium from neptunium



:means of preferentially oxidizing plutonium.

ple and' eifective means of separating neptunium from plutonium.

2,8383% latented June 10,1958

OXIDATIVE METHOD OF SEPARATING PLUTONIUM FROM NEPTUNIUM V Loren J.Beaufait, Jr., Richmond, Califi, assignor to the United States ofAmerica as represented by the United States Atomic Energy Commission NoDrawing. Application March'2 5, 1948 Serial No. 17,118 Claims. (Cl.23-145) d of separating nep- ;tion. they form insoluble complexacetates; with; alkali metals, and they are carried from solution assodium nep- .tunyl acetate and sodium plutonyl' acetate, especially.when sodium uranyl acetate is present as a carrier.

It is an object of this invention to provide anjeflicient It is also anobject of thisinvention to provide a composition comprising neptuniumessentially free of plutonium.

-It is a further object of this invention to provide a simof separatingneptunium from plutonium. e

A further object is to provide an improved fast method In accordancewith this invention neptunium is separated from a aqueous solutioncontaining neptunium and p111- tonium in valence states not greater than+4 by contacting said solution with dichromate. ions at below v50 C. andpreferably between to 30 C., thusgoxidizing' the neptunium to a valencestate greater than +4, without oxidizing any substantial amount ofplutonium,.'fand thereafter adding ions 'which form an, insolublecarrier precipitate which carries the plutonium from solution, leavingthe neptunium behind in the supernatant solution'. A preferredembodiment of this invention coniprises contacting the solution oxidizedas above with lanthanum ions and fluoride ions, thus precipitatinglanthanumfluoride and plutonium fluoride andthen separating theresultant precipitateand supernatant solution.

The operation of this invention is illustratedbylthe following examples.i

EXAMPLE I In this example an aqueous nitric acid solution containingplutonium and neptunium ions in valence states not greater than +4 wasmade 0.15 M in acetate ion, 0.19 M in acetic acid and 0.10 M in sodiumdichromate. The solution was then held at about 22 C. for variouslengths of time.

were made 0.8 M in nitric acid, and suflicient lanthanum ions in theform of lanthanum nitrate and fluoride ions oxidizingneptunium withoutAfter standing the samples of solution 05 in the form of hydrofluoricacid were added to form a precipitate of lanthanum fluoride. Thisprecipitation removes any unoxidized plutonium and neptunium in'thesolutions. The following table gives typical results.

' Time, .Percent Percent Uranyl concentration Min. ,7 up Np OxidizedOxidized In the above solutions tracer 50-year Pu and 2.3- day Np wereused. The quantities of these tracers in theoriginal solution and in thelanthanum fluorideprecipitates were determined by the usualradioch'emical techniques. The data show that an acid solution ofdichromate at room temperature will oxidize essentially :all of theneptunium to the fluoride-soluble state ,whileleaving most of theplutonium in a state of oxidation in which it is carried from solutionby lanthanum fluorides provided the oxidation is not too prolonged; Whenthe time of oxidation is as longnas two'and one-half hours, about 23% ofthe plutonium is oxidized under the conditions of this example.

" EXAMPLE II .v -The solutions employed were made up as followspdvvw ltann n Microliters Y "1 II'I IV Np tracer solution... I40 40 40 B0 .,Putracer solution 50 50 '50 7 50 50 100 200 300 310 260- 160 20 50 50 p 50Total volume.- 500 500 500 500 The chief differences in composition ofthesesolutions were in the quantity of nitric acid used. At. the closeof various time intervals 100 rnicroliter aliquots were withdrawn fromthe solutions and the extent of oxidation of the plutonium and neptuniumwas determined by the addition of lanthanum ions and fluorine ions inthepresence of 0.005 M uranylnitrate, thus forming a lanthanum fluorideprecipitate which carried the unoxidized plutonium from solution alongwith small amounts of neptunium.

After removal of the p passed through the solution to reduce theneptunium and any remaining plutonium to'fat least the +4 state ofoxidation; Following this reduction fluorine"ion's'"a'nd :lanthanum ionswere added in the order just stated, thus .yielding a lanthanumfluorideprecipitate. This'precipitate carried the i'plutonium which hadbeen previously 60 "oxidized by thedichromate along with the bulk of the.neptunium.. The plutonium in this precipitate was deterjmined byalpha-counting using the usual radiochemical techniques. The neptuniumin the first precipitate was Qdetermined'by beta counting using theusualradioehemical techniques. The results are given in Table 'I, which.shows thepercentages of plutonium and neptunium which had been oxidizedby the dichromate treatment.

3 I able I OXIDATION IN HNOr-NazOraOrSOLUTIONS A T 25' C.

Time of Oxidation Percent u Oxidized Percent Solution Aliquot NpOxidized III Iva "7?".-

IVb

The data of Table I show that when the nitric acid concentration was 1to 2 N the plutonium was slowly oxidized so that it did 'not carry wellwith the first lanthanum fluoride precipitate. However, when the nitricacid concentration was 4 to 6 N the plutonium remained largelyunoxidized and so carried well with the first lanthanum fluorideprecipitate. In all cases only relatively small amounts of the neptuniumremained unoxidized to carry down with the first lanthanum fluorideprecipitate.

EXAMPLE III In the third example oxidation of the neptunium was carriedout in H SO Na Cr O solutions. tions were made up as follows Volume inMieroliters I II III Np tracer solution i "0 Pu tracer solution- 5 50 5ON H2804 200 300 20 N H 801 200 Water V 190 95 180 1 M NazClaO 50 50 50Total Volnme.. 500 ,500 500 At the close of various time intervals 10()microliter aliquots were withdrawn from the solutions and the extent ofoxidation of the plutonium and neptunium was determined as described indetail in- Example II.

The detailed data are presented in Table II. They show that in 4 to 8 Nsulfuric acid solution the plutonium largely remains unoxidizcd andtherefore carries with the first lanthanum fluoride precipitate. Incontrast, the neptunium that remains unoxidized is less than 2% in allcases.

Table II OXIDATION IN HrSOr-NazCrzCh SOLUTIONS AT 25 C.

Time of Percent Oxidation Percent Solution N u Oxidized Aliquot pOxidized IIb mooooooaacacpazmmmcacnmvw ZZZZZZ-ZZZZZZZZZZmaeaammwiewnwsuumuwmu The solu- '4 -In both examples, II and III,whenthe acidity is 4 to 8 N, the rate of oxidation of plutonium bydichromate is sufiiciently slow that no appreciable losses of thiselement will occur in the lanthanum fluoride precipitation process evenif plant operation shutdowns of twenty-four hours or longer shouldoccur. Also the neptunium is sufficiently oxidized so that it does notcarry down with the plutonium. Higher acidity than 8 N may be used, suchas 16 N or higher, but preferably the acidity is kept below 7 N fornitric acid and below 10 N for sulfuric acid. The data presented showvthat a decontamination factor for neptunium of approximately 100 will beobtained in one I-I SO .Cr O-;- oxidation cycle.

While there have been described certain embodiments of my invention, itis to be understood that it is capable of-many modifications. Changes,therefore, may be made without departing from the spirit and scope ofthe invention as described in the appended claims.

What is claimed is: I

1. A process for the preferential oxidation of neptunium in an aqueoussolution containing neptunium and plutonium each in a valence state notgreater than +4 and mineral acid in a concentration of at least 4 N,comprising digesting said solution in the presence of dichromate ions ata temperature of below 50 C.

2. The process of claim 1 wherein the source of the dichromate ions isan alkali dichromate.

'3. The process of claim 1 wherein the source of the dichromate ions issodium dichromate.

4. The process of claim 1 wherein the solution is between 4 to 7 N innitric acid.

5. The process of claim 1 wherein the solution is between 4 to 10' N insulfuric acid.

6 A process for the separation of neptunium from plutonium in an aqueoussolution containing neptunium and plutonium each in an oxidation statenot greater than +4 and mineral acid in a concentration of at least 4 N,comprising contacting the solution with dichromate ions, then digestingthe solution at a temperature of 15 to 30 (2., adding lanthanum ions andfluorine ions whereby a lanthanum fluoride-plutonium-containingprecipitate is formed, and thereafter separating the supernatantsolution containing the'neptunium from. the precipitate containing theplutonium.

7. The process of claim 6 in which lanthanum nitrate is the source ofthe lanthanum ions and hydrofluoric acid is the source of fluorine ions.

8. The process of claim 6 wherein the acid is nitric acid.

9. The process of claim 6 wherein the acid is sulfuric acid.

10. A process for the separation of neptunium from plutonium in anaqueous solution containing neptunium and plutonium each in a valencestate not greater than +4, nitric acid in a concentration not greaterthan 1.0 M, acetic acid and sodium acetate, comprising treating thesolution with dichromate ions, digesting the solution at 15. to 30 C.whereby the neptunium is selectively oxidized, then treating thesolution with a lanthanum fluoride precipitate, thereafter separatingthe plutonuim-containing precipitate from the supernatant solution.

References Cited in the file of this patent Seaborg et al.: Journal ofthe American Chemical Soc.,

1. A PROCESS FOR THE PREFERENTIAL OXIDATION OF NEPTUNIUM IN AN AQUEOUSSOLUTION CONTAINING NEPTUNIUM AND PLUTONIUM EACH IN A VALENCE STATE NOTGREATER THAN +4 AND MINERAL ACID IN A CONCENTRATION OF AT LEAST 4 N,COMPRISING DIGESTING SAID SOLUTION IN THE PRESENCE OF DICHROMATE IONS ATA TEMPERATURE OF BELOW 50*C.